Sony XM-GS6DSP Mode D'emploi page 11

 Line input connection 
(for Subwoofer BTL system/6ch mode)
With the speaker connection  or  (page 14)

Notes
 When making this connection, set the SELECT switch
to the "6ch" position.
 Make sure the signal to SUB AUDIO IN is monaural.
SUB AUDIO IN of this unit does not support stereo
signal input.
 Line input connection 
(for 3-way speaker system/6ch mode)
With the speaker connection  (page 15)
RCA splitter cable
(not supplied)

Note
When making this connection, set the SELECT switch to
the "6ch" position.
* Use an RCA splitter cable (not supplied) to branch the
signals from REAR AUDIO OUT to REAR AUDIO IN and
SUB AUDIO IN.
11
GB